flush request is issued in transaction commit code path usually, so
looks using
GFP_KERNEL to allocate memory for flush request bio falls into the classic
deadlock issue (memory reclaim recursion). Use GFP_NOFS to avoid recursion
from reclaim context. Per Dave Chinner, there is only blkdev_issue_flush
might
be buggy here. But using GFP_NOFS by default for all calls should not
matter.
Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
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